1. Field of the Invention
The present invention relates to a biological treatment apparatus for wastewater, and more particularly to a biological treatment apparatus for wastewater adopting the activated sludge process.
2. Description of the Related Art
Biological treatment is a secondary procedure of wastewater treatment, which is typically employed for the wastewater being primarily treated. The wastewater from the primary sedimentation tank is biologically treated and settled, and then discharged. The organics contained in the wastewater is degraded by means of biological metabolism, so as to remove the organics (the so-called biochemical oxygen demand, BOD, and chemical oxygen demand, COD) as well as nitrogen compounds and phosphorous compounds therefrom.
Typically, the biological treatment is classified into such as aerobic treatment and anaerobic treatment. The aerobic treatment is carried out to remove the organic carbon from the wastewater and to make the organic nitrogen and ammonia nitrogen bio-oxidize into nitrates. The removal of nitrates from wastewater is carried out by means of anaerobic treatment, which is so-called as denitrification. The microbes employed in biological treatment are consisting of bacteria, fungus, algae and protozoa, where the community thereof shall be well-acclimated for various kinds of wastewater to be treated and substances to be removed. It is so difficult to well-control the treatment efficiency, since the treatment efficiency is highly depending upon the community of microbes and treating condition. In this case, the operation of such process is much complicated and needs technicality.
In an activated sludge process, which is one kind of aerobic treatment, wastewater being primarily treated is directed into an aeration tank to contact and mix with the activated sludge therein, and is subsequently directed therefrom into a settlement tank for sludge separation. A portion of the separated sludge is returned into the aeration tank (i.e. the returned sludge) while the remaining portion thereof is discharged to be further processed (i.e. subjected to the so-called sludge treatment and disposal). In addition to the difficulty in acclimation of microbial community, it needs to precisely control a variety of factors and conditions, such as the retention time, the return ratio of sludge, the aeration condition . . . etc. for the activated sludge process, so as to optimize the operation condition and achieve an improved efficiency.
Typically, the activated sludge composed of suspended aerobic microbial community is easily peeling off, which may cause the concentration of suspended solids of water and thus the loading of the activated sludge process to significantly increase. Moreover, the peeling-off of microbial aggregation also makes the control of operation condition of such process much difficult.
Due to the selectivity nature of biological degradation, it is necessary for the biological treatment to adopt multiple stages of sludge return and wastewater return for controlling the anoxic mode, anaerobic mode and aerobic mode in different reactors or tanks, so as to carry out the nitrification of ammonia nitrogen and removal of organic carbons (e.g. BOD and COD) under the aerobic condition, to carry out the denitrification and removal of nitrate nitrogen under the anaerobic condition. Such process is also termed as an A2O process, which is complicated, land-consuming, and cost-inefficient.
On the other hand, the membrane separation process is commonly used in treating the industrial wastewater and municipal wastewater. Some membrane modules, such as microfiltration (MF) modules, are capable of being combined with the biological treatment for the bio-sludge separation in a membrane bioreactor (MBR), so as to obtain the effluent of good quality. Nevertheless, the suspended solids caused by the peeling-off of microbial aggregation as well as the adsorption of sludge floe onto the membrane may result in the membrane fouling, and hence the membrane needs to be frequently replaced or cleaned. Accordingly, such process is not cost-efficient and needs to be improved.